Method for removing substrates provided with organic coatings

ABSTRACT

The invention relates to a method for removing a substrate that is coated with an organic coated coating by means of ionogenic gel formation. In said method, a wet or dry organic coating that has not yet formed a film on the substrate is treated with an aqueous solution of a metal salt from main group I in the periodic table of the elements, a complexing agent and/or a basic compound having a pH value&gt;10.

The invention relates to a method for removing organic coatings fromsubstrates, the organic coating having been applied by means ofionogenic gel formation, and recycling of the substrate and also wherepossible of the detached coating.

Currently, it is not financially viable, or is only feasible withdifficulty, to remove the deposited varnish layer(s) of dip-coatedsubstrate before firing. Defectively coated substrates are generallydisposed of or have to be reworked in costly processes. The document DE10 2013 201 966 A1 discloses a novel method for coating metallicsurfaces and the coating systems used for this purpose, by which adispersion of film-forming polymers and an anionic polyelectrolyte inthe form of an ionogenic gel is deposited by cations dissolved out ofthe metallic surface. The entire content of the aforementioned documentshould form part of the present application. The coating systemsdescribed therein are designated, in the context of this application, asuniversal dip coats.

The object of the invention is to provide a method by which the organiccoating formed by ionogenic gel formation can be removed again from thesubstrate surface by various chemicals, optionally by a dipping orspraying process, and the substrate can be reintegrated into the processchain for a repeated coating.

According to the invention the method for removing a substrate that iscoated with an organic coating by means of ionogenic gel formation iscarried out by treating a wet or dry organic coating that has not yetformed a film on the substrate with an aqueous solution of a metal saltfrom main group I in the periodic table of the elements, a complexingagent and/or a basic compound having a pH value>10.

The removal is preferably carried out using a dipping or sprayingprocess.

An aqueous solution of at least one metal salt of the elements Li, Naand K as well as preferably Na and K is preferably used.

Alternatively, a complexing agent is used which undergoes substantialcomplexing with iron, zinc, magnesium and aluminum, preferably EDTAand/or polyethylenimine.

As a further alternative, aqueous solutions of NaOH, KOH and/or NH₃ areused as basic compounds.

The thickness of the coatings to be removed can range from a few nm toseveral μm. Preferably, however, the thickness of the coating to beremoved ranges from 1 μm to 100 μm, particularly preferably 5 μm to 35μm. In individual cases, such as for example a process shutdown or acontamination of the dip bath with metal ions, it is also possible toclean complete baths or blocked pipelines.

The concentration of the solution used is at least 5% w/w. However, aconcentration between 10% and 70% w/w is preferably used. The range isparticularly preferably between 20% and 45% w/w. The substances used canbe combined in any ratios into aqueous formulations.

Particularly preferably, the removal of wet films can be carried out.

According to the invention, after the removal of the ionogenic gelcoating the substrate can be used for coating again.

A pre-treatment by alkaline cleaning is preferably carried out beforethe substrate obtained is coated again.

Furthermore, the method according to the invention has the advantagethat it enables the reconditioning of the detached coating. Theresulting dispersion can be used again for ionogenic gel deposition onmetallic surfaces. The recycling of the detached and dissolved coatingcan be assisted by concentration and/or neutralization. The resultingwashing solution can be used either for reformulations or for alreadyexisting baths.

The invention is explained in greater detail below with reference tothree examples without the invention being limited thereby to theseexamples.

Example 1

bases

-   -   NaOH 10%    -   KOH 10%    -   NH₃ 15-25%

Example 2

competing metal ions

-   -   KCl    -   NaCl    -   K₂CO₃ 10%    -   Na₂CO₃ 10%    -   K₂SO₄ 10%

Example 3

complexing agents

-   -   Lupasol G20 15%    -   Lupasol FG 15%    -   EDTA (ethylene diamine tetraacetate)

The substances specified in the examples are prepared in aqueousformulations in the specified percentages by weight attached. Thensubstrates coated with an organic coating in terms of the ionogenic gelformation are dipped into the produced solutions and if required areswiveled slightly until the coating dissolves or is detached.

1. A method for removing from a substrate an organic coating previouslyapplied thereto by means of ionogenic gel formation, the method beingcharacterized in that a wet or dry organic coating that has not yetformed a film on the substrate is treated with an aqueous solution of ametal salt from main group I in the periodic table of the elements, acomplexing agent and/or a basic compound having a pH value>10.
 2. Themethod according to claim 1, characterized in that the removal iscarried out by either a dipping or a spraying process.
 3. The methodaccording to claim 1, characterized in that the metal salt is selectedfrom the group consisting of Li, Na, K, and a combination of Na and K.4. The method according to claim 1, characterized in that the complexingagent undergoes substantial complexing with iron, zinc, magnesium andaluminum.
 5. The method according to claim 1, characterized in that thebasic compound is selected from the group consisting of aqueoussolutions of NaOH, KOH and/or NH₃.
 6. The method according to any ofclaims 1 to 5, characterized in that a concentration of the metal saltin the aqueous solution is at least 5% w/w.
 7. The method according toclaim 1, characterized in that a concentration of the metal salt in theaqueous solution is between 10% and 70% w/w.
 8. The method according toclaim 7, characterized in that the concentration is between 20% and 45%w/w.
 9. The method according to claim 1, characterized in that wet filmis removed.
 10. The method according to claim 1, characterized in thatthe thickness of the coating is in the range of 1 μm to 100 μm.
 11. Themethod according to claim 1, characterized in that after the removal ofthe organic coating the substrate is re-coated.
 12. The method accordingto claim 11, characterized in that a pre-treatment is carried out beforethe substrate is re-coated.
 13. The method according to claim 1,characterized in that a concentration of the metal salt in the aqueoussolution is at least 5% w/w.
 14. The method according to claim 13,characterized in that wet film is removed.
 15. The method according toclaim 13, characterized in that the thickness of the coating is in therange of 1 μm to 100 μm.
 16. The method according to claim 13,characterized in that after the removal of the organic coating thesubstrate is re-coated.
 17. The method according to claim 16,characterized in that a pre-treatment is carried out before thesubstrate is re-coated.